This invention relates to the recycling of scrap automobile and truck tires into useful products.
Disposing of scrap tires has become a very large environmental problem. Millions of worn out automobile and truck tires are presently being stored in enormous piles or filling canyons. These piles result in visual pollution and sometimes catch fire, with the resulting large, dense, smoke plumes polluting the air for miles down wind. In addition liquid hydrocarbons may be released into the ground water due to pyrolitic reactions as the tires are heated, then burned. These tire pile fires are very difficult to extinguish.
Tires are presently being recycled on a very limited scale. Some are ground into particles useful in road building. Others are used in the creation of artificial reefs to improve lake and ocean fishing. Some are used for barriers around go-cart race tracks. Presently, recycling is consuming fewer tires than are being added to the waste stream.
Attempts have been made to recycle at least parts of tires into structural beams and the like. For example, Snyder in U.S. Pat. No. 5,096,772 describes a beam forming process in which the sidewalls of tires are cut away, the rubber tread portion is sliced away from the steel belts. A thin layer of rubber is vulcanized to the belts and the belts are laminated together. However, this process uses only a small percentage of the tire, requires a complex layup to assure that the tire cords are arranged in different directions in succeeding layers and is quite costly.
Tripp in U.S. Pat. No. 5,340,630 describes a process for recycling the tread portion of tires in which the sidewalls are cut away, the tread portions are joined end to end to form two elongated continuous plies, then the two plies are bonded together to form a long two-ply member. This member can be used as a building material. However, this process is limited to a two ply thickness, is subject to delamination and is not directly useful as a product other than in fabricating other structures.
Similarly, in U.S. Pat. No. 5,412,921, Tripp describes a method of making a structure similar to an I-beam from the elongated plies made in his earlier patent, with plies forming the faces of the I-beam and two plies together forming the I-beam flange. This is a complex, difficult to secure together, assembly. FIG. 6 of the Trip ""921 drawing clearly shows the curvature of tire treads that makes difficult the bonding of two plies together to form a double-ply member.
Miller discloses, in U.S. Pat. No. 5,472,750, a method of producing large, thick, mats from tires which includes the steps of slitting the sidewalls and pressing the tire flat to form a preform having a rectangular center area conforming to the tread and a saw-toothed edge corresponding to the sidewalls, then stacking and bonding these preforms. Problems remain in truly flattening the preforms due to lesser sidewall thickness relative to tread thickness. In particular, obtaining tight interlocking of the saw-toothed edges is difficult, since this pattern conforms to the sidewall diameter and sidewall diameters vary greatly.
In U.S. Pat. No. 5,834,083. Pignataro, Jr. describes a tire recycling process including removing sidewalls from the tires, cutting the tread transversely to form strips, fastening the strips with interlocking dovetails and bonding strips together. This process is difficult and requires high accuracy in cutting dovetails. Due to the curvature of the inner surface of the tread material, bonding is difficult and likely to result in bubble formation or central separation of the lamination.
In general, the bonding together of tire tread strips to form two or more ply laminations has been very difficult and likely to result in delamination in use as a structural member. The edges of the tread strips, which curve toward the sidewalls, have a lesser circumference. Or, said another way tread strip edges have a shorter length than the strip centerline when laid flat. This difference makes flattening the tread very difficult.
Therefore, there is a continuing need for improvements in guard rail systems that recycle portions of used tires, that are strong and resilient, are highly resistant to impact damage, that will not deteriorate when exposed to severe weather and freeze/thaw cycles and that can be provided with a reinforcing surface coating having any desired color.
The above-noted problems, and others, are overcome by a process for recycling scrap automobile, truck, etc., tires which basically comprises the steps of removing the tire sidewalls (which can be ground for road building particles or other uses), cutting the tread portion transversely to form an elongated strip, slitting the strip edges transversely inward toward the tread longitudinal centerline to a depth of about one inch to about the tread longitudinal centerline about every 1 to 4 inches to form a slat useful in manufacturing various structures. The slits. are preferably evenly staggered, with a slit on one side spaced equally between slits on the opposite side.
These slats may then be secured together in unitary pairs, then additional slats(individual or added unitary pairs) may be secured to both sides of the first unitary pair to provide any suitable number of tread laminations to produce the desired product thickness. While adhesive bonding of slats is optimum in most cases, producing an outstanding combination of strength, resiliency and resistance to separation, mechanical fasteners, such as staples or ring nails, may be used if desired. In some cases both adhesive bonding and mechanical fasteners may be used.
For many uses, it is desirable that the slats be trimmed to a selected width for an intended purpose. For example, automobile tires can be cut to a 6 inch width, with truck tires capable of producing slats having 7 to 10 inch widths. Automobile tires produce slats having lengths of approximately 5 to 8 feet, while truck tire slats have lengths of approximately 6 to 9 feet. These slats can be cut to any desired lesser length.
While a beam produced by laminating a plurality of slats may be used as is, in some cases further trimming to a desired configuration or to a desired thickness, width or length may be done. The beams may be laminated together in a staggered relationship to provide thick panels for use as walls or other structures. This laminate is useful in a wide variety of products and structures. Two particularly preferred product uses are parking stops of the sort presently generally made from concrete and posts and beams used in guard rails, due to the outstanding combination of overall strength, resiliency and impact energy absorption characteristics of the laminations.
The slats are laminated under high pressure, preferably from about 100 to 200 psi. Typically, a steel beam may be hydraulically pressed against the slats or beam in an open topped, box-like mold. While slats may have uneven thickness in some areas due to uneven side to side wear or other reasons, we have found that laminating at an elevated pressure will produce structures having substantially uniform thickness. The beam may have a plurality of holes through which mechanical fasteners, such as ring nails, can be inserted into the material being pressed.
The exterior of a laminated structure may coated with any suitable material to seal the surface and provide a desired color. In a particularly preferred embodiment, a coating of a high strength elastomer. This will provide an attractive surface of any desired color and will further reinforce the structure. With such a coating, staples or other mechanical fasteners are generally sufficient to secure the slats together.